The present invention relates to a manual transmission having a locking device for locking individual gears.
The locking device of a manual transmission primarily has the following functions:                a) Preventing two gears from being operated simultaneously. Specifically the shifting channel of gears 3/4 is not selected cleanly during a fast shifting from the second to the third gear, that is, when a shift takes place “between the shifting channels” 1/2 and 3/4, the shift forks or shift rockers of both shifting channels may be operated simultaneously.        b) Preventing that an additional gear from coming into a shifting engagement when one gear is engaged. This could occur by a “self-acting” displacement of sliding sleeves as a result of vehicle vibrations or when locking elements, which exercise forces on shift forks or shift rockers, are defective.        
DE 39 29 270 A1 discloses a manual transmission in which the sliding sleeves assigned to the individual shifting channels are in each case axially displaceable by way of a shift rod and a shift fork fastened thereto. In this transmission, the “locking device” is formed by a locking plate. The locking plate is arranged orthogonally to the shift rods and is slidably disposed in the transmission case in the plate direction. The individual shift rods extend through a recess provided in the locking plate and each have locking notches in which the locking edges of the locking plate engage. By means of the locking plate, it is ensured that only one of the shift rods is axially displaceable and the other shift rods are locked.
In the case of locking devices, a differentiation is made between “active” and “passive” locking systems. An active locking system is disclosed in DE 196 15 267 C1, wherein when a shifting channel is selected, only this shifting channel is opened up and the other shifting channels are locked. In contrast, in the case of a passive locking system, the locking will be “activated” only when the shift fork or shift rocker is shifted.
Bayerische Motoren Werke AG has a five-speed manual transmission with shift rockers in which for locking individual shift rockers three locking levers disposed in the transmission case are provided which are connected with one another in an articulated manner. An expansion of this “locking lever system” to a six-speed transmission is problematic. The reason is that, in the case of a six-speed transmission, an additional locking lever is required. This would lead to an addition of component tolerances and would be difficult to control constructively.
It is an object of the invention to provide a locking device for a manual transmission which has a simple construction.
An aspect of the invention relates to a “rod-type” locking element which extends in the axial direction along several operating elements and which, in the individual possible transmission shifting positions, engages in each case with some of the existing operating elements. When one of the operating elements is shifted from its neutral position into a shifting position, the “locking” rod is brought into a locking engagement at least with some of the existing operating elements; that is, these operating elements will then be locked. Since the locking takes place during the engaging of a gear; that is, when an operating element is operated, a “passive” locking device is present according to the above-mentioned terminology.
The “operating elements” may be shift rockers or shift forks. They have a “locking finger”. For locking the operating element, notch-type or groove-type recesses are provided on the locking rod, which recesses can be caused to engage with the respectively assigned locking finger.
The notch-type recesses may be provided on opposite longitudinal sides of the rod-type locking element. However, the recesses do not have to be provided on the exterior sides or longitudinal sides of the locking element.
In a variant of the invention, the locking element has several closed, for example, rectangular or oblong “shifting recesses” into which the locking fingers project and in which the locking fingers are longitudinally displaceable, that is, shiftable in certain positions. In this case, the notch-type recesses are provided on the lateral “edges” of the rectangular or oblong “shifting recesses”. In the top view, the notch-type recesses are not situated on the outer contour of the locking element but within its outer contour. The notch-type recesses therefore form a portion of the contour of the shifting recesses. If the locking element is a locking plate, the shifting recesses or the notch-type recesses may, for example, be punched.
The locking fingers of the operating elements assigned to the individual shifting channels are arranged in an “offset” manner. This means that some of the existing locking fingers are arranged on a first longitudinal side of the locking rod and the other locking fingers are arranged on the opposite longitudinal side of the locking rod. Preferably, the locking fingers of shifting channels situated side-by-side in the shifting diagram are alternately arranged on one or on the other longitudinal side of the locking rod.
In the case of the above-mentioned variant of the invention, in which the notch-type recesses form a portion of the interior contour of the oblong shifting recesses, the term “offset” is to be understood such that some of the notch-type recesses are provided on the left longitudinal sides of individual “oblong holes”, and the other notch-type recesses are provided on the right longitudinal sides of the other “oblong holes”.
The locking rod is fixedly arranged in the axial direction and is displaceably arranged in a transverse direction. It may be disposed to be transversely displaceable in the transmission case, for example, by way of a simple slide bearing. However, a “case-side” bearing is not necessarily required. Specifically, the locking rod may also be disposed exclusively by way of its “locking recesses” at the locking fingers of the shift rockers engaged at that time.
The recesses of the locking rod preferably each have two “function bevels” which converge in a V-shape. When all operating elements are in the neutral position and an operating element is shifted whose locking finger in the neutral position engages with a recess of the locking rod, when the operating element is shifted, this locking finger can slide on one of the function bevels out of the recess. The locking finger of the currently operated operating element in this case applies a “transverse force” upon the locking rod. The locking rod is laterally displaced by this transverse force. As a result of the shifting of the operating element from its neutral position into its shifting position and the thus caused lateral displacement of the locking rod, a portion of the locking fingers is lockingly engaged with the locking rod. The locking rod is therefore displaced exclusively by the moving of the operating elements. A separate operating device for the locking rod is therefore not required.
In comparison to “multi-member” locking devices, a “locking rod” according to the invention has the important advantage that very low component tolerances are achieved. Furthermore, no or only a few housing-side bearings are required.
The locking device according to the invention is also distinguished in that no connection exists between the shifting shaft, which is connected with the shift lever to be operated by the driver, and the locking rail. The “linear displacement” of the locking rail is therefore not induced directly by way of the shift lever or the shifting shaft connected therewith but exclusively by way of the locking fingers of the operating elements, that is, the shift forks or the shift rockers.
The operating elements and the assigned recesses in the locking rod are preferably arranged such that adjacent shifting channels in the “shifting diagram”, that is R and 1/2, 1/2 and 3/4 or 3/4 and 5/6, cannot be shifted simultaneously.
In a variant of the invention, a swivellably disposed “additional lever” is provided on each side of the locking rod. The additional levers are arranged such that the locking fingers of the shift rockers are situated between the locking rod and the respective additional lever. With such additional levers, it can be ensured that, with the exception of the currently operated shift fork or shift rocker, all other shift forks or shift rockers are locked.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.